U.S. patent application number 10/922383 was filed with the patent office on 2006-02-23 for acoustic fluid machine.
Invention is credited to Tamotsu Fujioka, Masaaki Kawahashi, Masayuki Saito.
Application Number | 20060037812 10/922383 |
Document ID | / |
Family ID | 35908611 |
Filed Date | 2006-02-23 |
United States Patent
Application |
20060037812 |
Kind Code |
A1 |
Kawahashi; Masaaki ; et
al. |
February 23, 2006 |
Acoustic fluid machine
Abstract
An acoustic fluid machine such as an air compressor comprises an
acoustic resonator, a valve device and a piston. Air is sucked into
the resonator through the valve device at one end of the resonator.
The piston at the other end of the resonator is reciprocated by an
actuator to compress the air in the resonator to cause resonance to
increase pressure of the air significantly. The inner surface of
the resonator is suitably curved to comply with the formula of a
half-period cosine function.
Inventors: |
Kawahashi; Masaaki;
(Saitama-shi, JP) ; Fujioka; Tamotsu;
(Yokohama-shi, JP) ; Saito; Masayuki; (Cincinnati,
OH) |
Correspondence
Address: |
DAVIS & BUJOLD, P.L.L.C.
FOURTH FLOOR
500 N. COMMERCIAL STREET
MANCHESTER
NH
03101-1151
US
|
Family ID: |
35908611 |
Appl. No.: |
10/922383 |
Filed: |
August 19, 2004 |
Current U.S.
Class: |
181/262 ;
181/220; 181/259 |
Current CPC
Class: |
F04F 7/00 20130101 |
Class at
Publication: |
181/262 ;
181/259; 181/220 |
International
Class: |
F01N 1/14 20060101
F01N001/14; F02K 1/00 20060101 F02K001/00; F02K 1/28 20060101
F02K001/28; F02K 1/38 20060101 F02K001/38; F02K 1/46 20060101
F02K001/46 |
Claims
1. An acoustic fluid machine comprising: an acoustic resonator; a
valve device comprising a suction chamber for sucking fluid from
outside and a discharge chamber for discharging the fluid from the
acoustic resonator at a first end of the acoustic resonator; and an
actuator comprising a piston at a second end of the acoustic
resonator, said piston being reciprocated to generate resonance in
the acoustic resonator to greatly increase pressure of the fluid,
an inner surface of the acoustic resonator being formed by a curve
in which variation rate of a cross-sectional area is zero at the
first and second ends of the acoustic resonator, said curve
gradually increasing and decreasing at substantially the same
gradients between the first and second ends.
2. An acoustic fluid machine as claimed in claim 1 wherein the
curve of the inner surface complies with the formula of a
half-period cosine function.
3. An acoustic fluid machine as claimed in claim 2 wherein the half
period cosine function is represented by: r .function. ( x ) = r p
- r 0 2 .times. .times. cos .function. ( .pi. L .times. x ) + r p +
r 0 2 ##EQU2## where L is the length of the acoustic resonator;
r.sub.p is the radius of the second end of the acoustic resonator;
and r.sub.o is the radius of the first end of the acoustic
resonator.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an acoustic fluid machine
based on pressure variation by acoustic resonance and especially to
an acoustic fluid machine suitable for use as an air compressor, a
cooling compressor and a vacuum pump.
[0002] Recently acoustic compressors have attracted considerable
attention, the compressors being grounded on pressure variation of
large amplitude standing acoustic waves generated by resonance in
acoustic resonators.
[0003] An acoustic resonator that is important in an acoustic fluid
machine such as an acoustic compressor comprises a linear pipe
having an internal constant cross-sectional area in EP 0 447 134
A2, and a conical pipe in which an internal cross-sectional area
varies in U.S. Pat. No. 5,319,938 A and EP 0 570 177 A2.
[0004] When a linear pipe is used as acoustic resonator, waveform
becomes steeper owing to nonlinearity with increase in amplitude to
generate propagating shock waves in the acoustic resonator. Thus,
increase rate of pressure amplitude in the acoustic resonator with
respect to amplitude increase in a driving source decreases rapidly
to cause acoustic saturation.
[0005] When a conical pipe is used as acoustic resonator, shock
waves are suppressed, and larger pressure variation amplitude in
the acoustic resonator is obtained in proportion to input amplitude
increase of the driving source.
[0006] However, it is difficult to obtain industrially applicable
pressure ratio in the linear or conical pipe, and resonance area is
variable with variation in acceleration of the driving sound source
depending on temperature change. Specifically, resonance points are
likely to be shifted, so that it is difficult to keep resonance
points, which results in difficulty in obtaining a stable acoustic
compressor.
SUMMARY OF THE INVENTION
[0007] In view of the disadvantages in the prior art, it is an
object of the present invention to provide an acoustic fluid
machine comprising an acoustic resonator to reduce waveform strain
and variation in resonant frequency with elevated piston
acceleration, thereby achieving stable resonant frequency with
respect to driving force amplitude corresponding to operational
conditions such as flow rate and pressure as a compressor, to
facilitate control in resonance points.
BREIF DESCRIPTION OF THE DRAWINGS
[0008] The above and other features and advantages of the present
invention will become more apparent from the following description
with respect to embodiments as shown in accompanying drawings
wherein:
[0009] FIGS. 1 (a), (b) and (c) are three graphs which show
relationships between length and diameter of acoustic resonators of
a conical pipe, an exponential-function-shaped pipe and a
half-cosine-shaped pipe respectively;
[0010] FIG. 2 is a graph which shows relationship between length
and cross-sectional area variation rate of the acoustic resonators
of FIG. 1;
[0011] FIG. 3 is a vertical sectional view which schematically
shows one embodiment of an acoustic compressor according to the
present invention;
[0012] FIG. 4 is a graph which shows relationship between time and
pressure at the closed suction/discharge end of the conical
pipe;
[0013] FIG. 5 is a graph which shows relationship between time and
pressure at the closed suction/discharge end of the
exponential-function-shaped pipe;
[0014] FIG. 6 is a graph which shows relationship between time and
pressure at the closed suction/discharge end of the
half-cosine-shaped pipe;
[0015] FIG. 7 is a graph which shows relationship between piston
acceleration and pressure ratio of the three different pipes;
[0016] FIG. 8 is a graph which shows relationship between frequency
and pressure at different piston accelerations when the acoustic
resonator comprises the conical pipe;
[0017] FIG. 9 is a graph which shows relationship between frequency
and pressure at different piston accelerations when the acoustic
resonator comprises the exponential-function-shaped pipe; and
[0018] FIG. 10 is a graph which shows relationship between
frequency and pressure at different piston accelerations when the
acoustic resonator comprises the half-cosine-shaped pipe.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] FIG. 1 shows three types of acoustic resonators in which (a)
and (b) are known and (c) is the subject of the present
invention.
[0020] (a) A conical pipe: Variation rate in diameter axially is
constant.
[0021] (b) An exponential-function-shaped pipe: Variation rate in
diameter at a larger-diameter actuating end is large, while being
small at the smaller-diameter suction/discharge end.
[0022] (c) A half-cosine-shaped pipe in which the inner surface of
the acoustic resonator is defined to comply with the formula of a
half-period cosine function: Variation rate in diameter is
substantially zero at the larger-diameter actuating end and the
smaller-diameter suction/discharge end.
[0023] With respect to the three pipes, variation rate in
cross-sectional area in an axial direction is shown in FIG. 2.
[0024] FIG. 2 means the following. In the conical pipe, the
cross-sectional area reduces linearly in an axial direction. In the
exponential-function-shaped pipe, the cross-sectional area reduces
steeply and then gradually. In the half-cosine-shaped pipe,
variation rate in cross-sectional area is zero at each end,
gradually increase from zero and gradually decreases to zero in an
axial direction.
[0025] An embodiment of an acoustic compressor according to the
present invention will be described with respect to a vertical
sectional front view in FIG. 3.
[0026] The acoustic compressor comprises an actuator 1, an acoustic
resonator 2 and a valve device 3.
[0027] The internal shape of the acoustic resonator 3 is defined by
the following formula: r .function. ( x ) = r p - r 0 2 .times.
.times. cos .function. ( .pi. L .times. x ) + r p + r 0 2 ##EQU1##
where L is the length of the resonator; r.sub.p is the radius of
the actuating end of the resonator; and r.sub.o is the radius of
the suction/discharge end of the resonator.
[0028] The actuator 1 functions also as support and includes a
piston 11 movable up and down by a suitable actuating unit (not
shown). A sealing member 12 is fitted on the outer circumference of
the piston 11.
[0029] The acoustic resonator 2 has an outward flange 21 which is
put on the upper surface of the actuator 1 and fastened by a bolt
22. The valve device 3 comprises a suction chamber 34 and a
discharge chamber 38. The suction chamber 34 has an inlet 31 at the
outer side wall and a sucking bore 33 with a check valve 32 at the
bottom, and the discharge chamber 38 has an outlet 35 at the outer
side wall and a discharge bore 37 with a check valve 36.
[0030] The check valves 32,36 comprise reed valves of thin steel
plates attached to the lower surface of the bottom of the suction
chamber 34 and to the upper surface of the bottom of the discharge
chamber 38, or rubber-plate valves.
[0031] The piston is made of Al and connected to the actuating unit
(not shown) to reciprocate axially at high speed with very small
amplitude at the larger-diameter actuating end of the acoustic
resonator 2. A driving frequency of the actuating unit is
controlled by a function synthesizer and adjusted with accuracy of
about 0.1 Hz.
[0032] The piston 11 is reciprocated with very small amplitude
axially at the larger-diameter end of the resonator 2. When
pressure amplitude in the acoustic resonator 2 becomes very small,
external air is sucked into the suction chamber 34 through the
inlet 31 and sucked into the acoustic resonator 2 through the
sucking bore 33 and the check valve 32. When pressure amplitude in
the acoustic resonator 2 becomes very large, the pressurized air is
passed into the discharge chamber 38 through the discharge bore 37
and the check valve 36 and discharged through the outlet 35.
[0033] The results of experiments will be described.
[0034] The initial condition provides room temperature of about
15.degree. C. and atmospheric pressure.
[0035] FIGS. 4 and 5 show relationship between time and pressure at
the closed end of acoustic resonator at piston acceleration of 100
m/s.sup.2, 300 m/s.sup.2 and 500 m/s.sup.2 when the acoustic
resonator is a conical pipe and an exponential-function-shaped pipe
respectively. Pressure waveform strain significantly reveals as
piston acceleration increases. As a result, with respect to initial
pressure, positive amplitude becomes unsymmetrical with negative
amplitude.
[0036] In contrast, FIG. 6 shows relationship between time and
pressure with respect to a half-cosine-shaped pipe and makes sure
that pressure waveform is substantially symmetrical.
[0037] FIG. 7 shows relationship between piston acceleration and
pressure ratio on three different pipes. The pressure ratio becomes
the maximum at the half-cosine-shaped pipe in which the minimum
pressure is the lowest in the three pipes.
[0038] FIGS. 8 to 10 show relationship between frequency and the
highest pressure amplitude when the frequency in the vicinity of
resonance points varies from the lowest to the highest and vice
versa with three kinds of accelerations, 100 m/s.sup.2, 300
m/s.sup.2 and 500 m/s.sup.2. In the conical pipe and the
exponential-function-shaped pipe in FIGS. 8 and 9 respectively,
with increase in acceleration, the pressure curves are gradually
inclined toward the higher frequency region.
[0039] So resonant frequency varies with acceleration of the
piston, and hysteresis of pressure amplitude variation with respect
to frequency variation was observed especially in the conical
pipe.
[0040] In comparison, in the half-cosine-shaped pipe in FIG. 10,
variation in resonant frequency depending on acceleration was not
observed and resonant frequency did not vary with increase in
acceleration of the piston.
[0041] Hence, variation in resonant frequency is small in the
half-cosine-shaped pipe to facilitate control on resonance points
when it is used as an acoustic compressor.
[0042] The foregoing merely relates to embodiments of the
invention. Various modifications and changes may be made by a
person skilled in the art without departing from the scope of
claims wherein:
* * * * *